Acute renal failure (ARF) is a common life threatening complication following allogeneic hematopoietic stem cell transplantation (HSCT). Non-myeloablative HSCT, a newer less toxic alternative, is being performed mainly among older individuals and patients with organ dysfunctions who have contraindications to conventional allogeneic HSCT. Non-myeloablative HSCT is relatively safe and well tolerated compared to the traditional allogeneic HSCT because of lower-intensity conditioning therapy used before transplant. Due to promising outcomes and safety of non-myeloablative HSCT, this procedure is increasingly used to treat hematologic malignancies and has enormous potential for treating a variety of diseases. To date there has been no systematic analysis of complications, like ARF, occurring in this group of patients. The goal of this proposal is to study ARF in a large group of patients who have received non-myeloablative HSCT. We have the access to the largest population of relatively uniformly treated patients undergoing non-myeloablative HSCT allowing us to address this important question. Four major university centers (University of Seattle, University of Colorado, Stanford University and University of City of Hope) have agreed to collaborate in this project. This combined data from the four centers will be used to determine the risk of ARF in these group of patients. Using multivariate analysis, predictors of ARF in this population will be established. Following this, regression models will also be constructed to determine if ARF independently predicts mortality. The results will better characterize these patients, will explore the important determinants of ARF, and may provide insights into the development of interventions targeted specifically at improving outcomes in this population. Our ultimate objective after finishing this epidemiological study is to design an interventional study to decrease the severity and incidence of ARF so as to attenuate the morbidity and mortality associated with non-myeloablative HSCT.